Bonding leads are understood in this context as meaning any kind of contacting of the contact areas of the semiconductor chip or the contact terminal areas of a wiring component serving for the onward routing of electrical supply lines and/or electrical signal lines. A wiring component of this type may also have bonding leads, which are used in many power semiconductor devices to transport electrical currents by means of bonding wires from an active upper side of a semiconductor chip to corresponding contact terminals or to corresponding contact terminal areas of a wiring component. In this case, the overall cross section of bonding wires of this type restricts the maximum current handling capability of the device as a whole.
In the document JP 2000 082721-A, copper links are used in a MOSFET power semiconductor device in place of aluminum bonding wires, with the effect of increasing the current handling capacity. However, copper links of this type have the disadvantage that they have to be specifically designed and adapted for each contact area of a semiconductor chip. Furthermore, process control is more expensive than in the case of simply increasing the number of bonding leads or bonding wires in a semiconductor device.
The document EP-A-0 265 927 discloses arrangements which optionally have a number of bonding wires arranged one on top of the other on a contact area of an active upper side of a semiconductor chip or on corresponding contact terminal areas of a wiring component. The bonding wires in this known document are made of gold. However, gold bonding wires with a diameter of between 20 μm and 50 μm are not recommendable for power semiconductor components in comparison with aluminum bonding wires of 50 μm to 600 μm. On the one hand, to achieve the same cross section, a large number of gold bonding wires would be required for wiring of the semiconductor chip, which quickly brings this technology to its limits, and on the other hand solid thick gold bonding wires of around the same size as aluminum wires are a cost factor which would disadvantageously escalate the costs for the production of power semiconductor devices of this type.
The document DE 1 032 40 69 A1 discloses a circuit arrangement with a method for the conductive connection of contact areas on semiconductor chips. Aluminum bonding wires are also used in the case of this publication for power semiconductor devices, the bonding leads being stacked in order to reduce the required chip contact areas, which for aluminum wires with a diameter of 600 μm already need a considerable amount of space on a semiconductor chip in order to electrically connect the semiconductor chip to a wiring component even in the stacked state. While the bonding leads are stacked one on top of the other on the semiconductor chip, since the available area of the semiconductor chip is relatively small in comparison with the available area of a wiring component, the bonding wires on the contact terminal area of a wiring component may well be arranged next to one another, in that the bonding wires are correspondingly splayed out from the common contact area and attached on a larger area of the contact terminal area of the wiring component.
Nevertheless, it has been found that bonding wire stacks of this type, whether for power semiconductor devices with stacked aluminum bonding wires or for signal-processing semiconductor devices with thin stacked gold bonding wires, represent a risk to the formation of a low contact transition resistance, especially since bonding of aluminum bonding wire on aluminum bonding wire or of gold bonding wire on gold bonding wire or of copper bonding wire on copper bonding wire is used in the case of the previously known stacking technologies. One disadvantage that has been observed with these stacked bonding leads is that the boundary layers between the contact elements sometimes become brittle on account of the susceptibility of copper and/or aluminum bonding wires to oxidize. Another disadvantage is that, during bonding, the relatively high melting temperatures of these metals must be reached in a locally restricted area, which can likewise have disadvantageous effects on the properties of the stacked bonding leads and on the monocrystalline semiconductor material lying there under or the material of the wiring component.